Pressure relief rupture disks are widely used as a pressure release safety device in containment vessels subject to positive or negative fluid pressure. The rupture disk is normally mounted in a pressure or vacuum relief conduit extending from the containment vessel. Based on the expected pressure/vacuum operating pressures and the recommended pressure limits of the containment vessel, a rupture disk is chosen having an appropriate burst pressure.
If the pressure differential on the rupture disk exceeds the burst pressure of the disk, the disk will burst thereby decreasing the pressure or vacuum in the vessel and avoiding catastrophic failure. A rupture disk monitoring apparatus is often used in conjunction with a disk. The monitoring apparatus detects rupture of the disk and activates an alarm so that appropriate action may be taken to shut down the system, correct the condition creating the excessive vessel pressure or vacuum and install a new rupture disk.
Various pressure relief rupture disk monitoring apparatuses have been proposed for detecting the rupture of a disk and activate an alarm indicator. One such prior art monitoring apparatus uses a conductive rupture disk as part of an electrical circuit. Spaced apart electrodes are attached to the disk. The electrodes are suitably coupled to a voltage source to complete the circuit. When the disk ruptures, the resistance of the disk is expected to increase to a large value, essentially infinity, resulting in an open circuit. The open circuit condition triggers activation of an indicator alarm.
In certain fluids, bursting of the disk will not result in an open circuit condition. If the fluid in the containment vessel is electrically conductive and the rupture of the disk is accompanied by presence of the fluid in the "gap" between the electrode ends, the assumption of infinite resistance between the electrodes when the disk ruptures is incorrect. Current can flow through the fluid in the "gap" region to prevent an open circuit condition from being sensed so that the alarm indicator will not be activated.
A pressure relief rupture disk monitoring apparatus must be reliable, rugged and adaptable to work in a variety of fluids, including fluids having a substantial electrical conductivity. Furthermore, the monitoring apparatus must be easy to install and require minimal maintenance. Finally, to be successful in the marketplace, the rupture disk monitoring apparatus must be competitive in price with other monitoring devices.